Please Observe Air Condition Cycle

[Roker]

Could someone please observe this on their Avensis and confirm the following:

With the air con. fully on/loaded on a cool day (12deg C) does the compressor turn on and off approx every 5 to 10 sec, you can feel the compressor pumping by just feeling the HP pipe where it exits the
compressor.

I cannot seem to get a straight answer to this, as to if it is normal or not. My system has always done this and the air seems to be cooling OK. It would make sense to me that the compressor would unload if it is not working hard, the same as an air compressor would switches on and off.

My LP pressure cycles between 10 and 40 psi.

[Call me Ishmael]

Hello Roker,

I've noticed something similar on my 2004 Avensis D4D. About every 5-10 seconds the engine comes under a very light load when idling. The revs don't dip, but there's definately something cutting in and out which I always assumed was the A/C compressor - if that helps.

[Roker]

Thanks Ishmael, you may find that the fan cuts in and out at the same time as the Compressor. Can anyone else also confirm this? just in case we both have the same fault. I would think in hot weather that the on and off frequency should decrease.

[Roker]

There doesn't seem much interest in this, it will only take 5 mins to try this for me, possible yours does the same

[Red Yaris 54]

Just like your refrigerator at home the Car Air Conditioning system will cycle on and off to maintain the cool air in your car

It is not necessary for the compressor to be working constantly to cool the air

[Roker]

As the Toyota has a Variable Displacement Compressor (no clutch) I thought it would not shut off, it should be able to adjust to zero displacement.

[Konrad C]

My air-con in my old 7A-FE works well, used it yesterday.

Like other posters have said, the system cuts in and out depending on the fan speed setting and/ambient temperature. At full speed it stays on more, whilst at the lowest speed, it cuts out more.

I don't think there is anything wrong with your system.

Now if it did not work at all, the air barely gets cold or the compressor bearings rattled when off, then there is a problem.

[Roker]

I did not get much response or help from others to see if their ACs cycles on off. (how difficult can it be)

As an update, I topped my system up with one of those Halfords kits, it did raise the pressure and preventing dropping to 10 psi. It stills cycles but a lot less, I was afraid to top up above 40psi in case I overfilled. As the air is quite cold from the vents and there is a good amount of heat going to the condenser, I will have to assume it is correct and to live with it.

It should be noted that if you use one of these Halfords kits, a AC specialist does not want to touch your system because of the leak sealer in the gas, which can bung up their equipment. Although not legal, all the pressure must be out of the system before they will look at it.

[Red Yaris 54]

I did not get much response or help from others to see if their ACs cycles on off. (how difficult can it be)

As an update, I topped my system up with one of those Halfords kits, it did raise the pressure and preventing dropping to 10 psi. It stills cycles but a lot less, I was afraid to top up above 40psi in case I overfilled. As the air is quite cold from the vents and there is a good amount of heat going to the condenser, I will have to assume it is correct and to live with it.

It should be noted that if you use one of these Halfords kits, a AC specialist does not want to touch your system because of the leak sealer in the gas, which can bung up their equipment. Although not legal, all the pressure must be out of the system before they will look at it.

You did get a response from some members. On here telling you that your system was normal

Maybe that is not what you wanted to hear?

Pleased that you have got your system so that you can now live with it :)

[Roker]

I got what people think should happen, wrongly assuming the Avensis had a clutch on the compresssor. I did not get people checking what their own car does when actually running (with a recently topped up system)

As I explained previously, it does not have clutch, it has a variable displacement compressor and can go to zero displacement, mine goes switches 0% to 100% instead of variable between 0% and 100%.

I was also trying to warn people the pitfalls of using the Halfords system

[Roker]

Response from professional AC repairer

I thought that all the 2005 Avensis used very similar electronically controlled variable displacement compressors. Using the 1.8 litre v v t i as an example which has this type of compressor. If yours is similar I am surprised that you could detect so great a disparity in the operation as the compressor is controlled by the AC Control Module via a variable width square wave signal.

If yours has this type of compressor then I would suggest that you have the control wire plugged into an oscilloscope to see what the compressor is being ordered to do.

I would expect the signal to initially be a maximum capacity signal gradually reducing to a much smaller capacity signal after several minutes. It may be of course that the correct square wave signal is being sent but the Electronic Mass Control Valve in the compressor is sticking and instead of reducing the flow is cutting it right off and then opening fully again.